Fuel cells are well known as devices for converting chemically-stored energy directly into electricity. One such type of fuel cell employs a solid-oxide electrolyte having a cathodic layer deposited on a first surface and an anodic layer deposited on a second and opposite surface. Oxygen atoms are reduced to O−2 by the cathodic layer, migrate through the electrolyte, and unite with protons produced from hydrogen by the anodic layer to form water, and, in the case of reformed gasoline, with CO to form CO2. Electrons flow from the anode via an external path to the cathode through the cell interconnect.
A plurality of such fuel cells may be assembled in series to form a fuel cell stack. The individual fuel cells are electrically connected to each other by interconnect elements between the electrodes to maintain electrical continuity. Each interconnect is mechanically and electrically connected on one side through a fuel flow space to an adjacent anode and on the other side through an air flow space to an adjacent cathode. Such connection is known to be provided by incorporation of conductive filaments or metallic sponge in the respective gas flow spaces between the electrodes and the interconnects.
Oxygen is provided to the cathode surface, typically in the form of air, in abundance as a coolant as well as an oxidant for the fuel cell. Fresh air is introduced via a first inlet manifold means to the air flow space at an entry edge of the cathode surface, flows across the surface, and is removed via a first exit manifold at an exit edge of the cathode surface. Hydrogen-containing gas is introduced via a second inlet manifold means to the fuel flow space at an entry edge of the anode surface, flows across the surface, and is removed via a second exit manifold at an exit edge of the anode surface. Typically, but not necessarily, such a fuel cell is rectangular in plan view, and the oxygen and fuel flow through the fuel cell orthogonally to each other.
A serious problem is known in the art which adversely affects both fuel utilization efficiency and electrical output of the cell or stack. The anode surface near the entry edge is exposed to fresh fuel with no combustion byproducts in it, such as H2O and CO2. Thus, the reaction rate and electricity production is relatively high in this region of the anode. However, as the fuel sweeps across the anode toward the exit edge, it picks up, and becomes diluted by, such byproducts while simultaneously becoming relatively depleted of H2 and CO. Thus, the reaction rate and electricity production become progressively reduced in anode regions farther from the entry edge. Because of this phenomenon, these regions of the anode are sub-optimized, or under-utilized, in production of electricity.
Further, a relatively large and potentially damaging temperature difference may result between high-reaction and low-reaction areas of the anode.
Therefore, there is a strong need for an improved means for distributing fuel more uniformly over all portions of the anode surface.
It is a principal object of the invention to improve temperature uniformity within a fuel cell.